DI-27
10
Key Design Points
• Design bias winding circuit to provide 250 µA to 300 µA
at no-load.
• Ensure C5 is large enough to supply above current at the
very low no-load switching frequencies.
• Minimize secondary circuit bias currents. Use low current
feedback Zeners for best tolerance.
• ZenerorRCDclampcanbeusedtoslightlyreduceno-load
consumption further. Use a 200 V Zener or maximize
resistor value in RCD clamp for lowest losses.
• Designtransformerwithlowreflectedvoltagetominimize
clamp losses.
• Wind transformer for lowest leakage inductance. Choose
wire gauges to completely fill winding layers.
• Wind transformer with tape between primary layers to
further reduce intra-winding capacitance.
8
6
4
2
Zener Clamp
RC Clamp
0
80
120
160
200
240
AC Line Voltage (A)
Figure 3. No-load Input Power Variation with Input Voltage.
100
TRANSFORMER PARAMETERS
VIN = 100 VAC
VIN = 230 VAC
EE16
Nippon Ceramic NC-2H
AL of 74 nH/T2
Core Material
Bobbin
EE16 10 pin
(Ying Chin YC1607 or equivalent)
10
Primary (1-2), Tape
12 V (10-9), Tape
Bias (3-4), Tape
Winding Order
(pin numbers)
Primary Inductance
3.67 mH ±10%
500 kHz (minimum)
300 µH (maximum)
Primary Resonant
Frequency
1
0
100
200
300
400
500
Leakage Inductance
BYPASS Pin Current (µA)
Figure 2. No-load Input Power vs. BYPASS Pin Current.
Table 1. Transformer Construction Information.
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Integrations’ patents may be found at www.powerint.com.
The PI Logo, TOPSwitch, TinySwitch and EcoSmart are registered trademarks of Power Integrations, Inc.
PI Expert is a trademark of Power Integrations, Inc. ©Copyright 2002, Power Integrations, Inc.
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